|Chip Amps Amplifiers based on integrated circuits|
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|24th August 2005, 08:24 AM||#1|
Join Date: Apr 2002
AD815 pre-amp driving gainclone
I've built the Ad815 pre-amp based on Carlosfm's schematics
(re)searching for a better preamp
and thought I'd share my experiences:
1. Sound is marvelous-Soundstaging is huge.
2. Vs the 627/634 combo, highs are more resolved, smoother, more extended, more enjoyable.
3. Bass is deeper as well. The one characteristic that stands out is the impression of "drive", especially in the upper bass.
4. Construction is relatively straightforward.
5. Using a nulling circuit, DC output can be reduced to zero.
1. The chip is only available as a 24-pin surface mount component. Not a problem if you can fabricate your own PCB's-I simply made a SOIC-DIL adapter and it works like a charm. The SOIC footprint allows the use of SM components (caps, resistors), which could bring noise benefits because of the small feedback loop etc.
1. For two weeks I struggled to get the Ad815 to work consistently with my monoblocked 3875 gainclone. In my initial configuration, the ground of the AD815 pre was coupled to the Ac ground for the amp.
The pre was ENORMOUSLY sensitive to positioning, volume pot adjustments, the phase of the moon, etc. humming at the drop of a hat and seeming to pick up all sorts of inteference, including transformer magnetic fields etc-drove me insane for a while trying to understand the problem.
The BIG lesson out of all of this was: Ensure that your amp has a ground connection to chassis. I tied the amp gnd and pre-amp gnd (which were connected to Ac mains gnd) to the chassis and since then the pre has been working perfectly.
My 2c for anyone trying this fantastic little chip.
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